Objectives: This 2 phase prospective and controlled trial examines the practicality, benefit and safety of paramedic administration of thrombolytic therapy. We will determine whether paramedics can select appropriate candidates for thrombolytic therapy and if pre-hospital thrombolytic therapy results in greater preservation of left ventricular myocardium than when treatment is initiated in hospital. A registry of all patients hospitalized with acute myocardial infarction will determine the proportion seeking paramedic care and what if any basic clinical differences exist between these patients and those arriving at hospital by other means in order to put the findings in the trial in perspective. Rationale: There is a growing concensus that the sooner coronary revascularization is effected following thrombolytic occlusion, the higher the resultant ejection fraction and lower the mortality. The safety and benefit of prehospital administration of thrombolytic treatment is unknown. Design: 1. The initial phase will examine whether paramedics can identify appropriate candidates for thrombolysis. 2. During the second phase, prehospital patients meeting the case definition (history and physical exam and ECG criteria) will be considered for thrombolytic therapy. Half will receive rt-PA initiated by paramedics and half will have the diagnostic information forwarded to the receiving hospital and treatment will be initiated there. Ejection fraction and myocardial perfusion defect size will be determined in both groups. Clinical histories, outcome and complication rates will be determined. A myocardial infarction registry will tabulate the proportion seeking paramedic care, and compare basic clinical findings in paramedic treated patients with those arriving at hospital by other means.